Temperature sensor forming method

ABSTRACT

A temperature sensor forming method and forming die are provided which perform insert-forming of a temperature sensor with a minimum of processes and in a short time. The temperature sensor formed has a temperature sensing element 1 arranged in a predetermined position inside a resin case 2. The process does not leave traces of pins that would allow water to penetrate the interior of the case. The process comprises a first step of supporting the temperature sensing element 1 with first and second slide blocks 6c and 6g. The process comprises a second step of injecting a molten forming resin 2a into a forming die 6 and retracting the first slide block 6c by injection pressure while the temperature sensing element 1 is being supported by the second slide block 6g. The process comprises a third step of retracting the second slide block 6g while injecting the molten forming resin 2a into the forming die 6. The receiving area S1 of the first slide block 6c is larger than the receiving area S2 of the second slide block 6g.

This application is a divisional of application Ser. No. 08/711,940filed Sep. 4, 1996, now U.S. Pat. No. 5,827,440.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a forming method and forming die for atemperature sensor which is insert-formed with a resin.

2. Description of the Prior Art

A conventional sensor enclosed in a resin case is disclosed in PublishedUnexamined Japanese Utility Model Application No. H4-24032. In thisconventional sensor, a case is formed beforehand and a resin is pouredinto the case to enclose a temperature sensing element.

Another conventional temperature sensor is disclosed in PublishedUnexamined Japanese Patent Application No. H6129915, which has beenpreviously filed by the applicants of the present invention. Thisconventional temperature sensor will be explained with reference to FIG.4 of the drawings. In FIG. 4, a temperature sensor is shown having atemperature sensing element 1, a resin case 2, and a stopper portion 3.

The temperature sensing element 1 is a thermistor, for example, and isconnected to terminals 5 via parallel twin leads 4. These twin leads 4comprise two lead wires 4a arranged in parallel with a predetermined gaptherebetween. The twin leads 4 are integrated by being covered with acover 4b, and provide a certain amount of rigidity with respect toinjection molding pressure and outside force when set in a forming die.Also, the terminals 5 have connecting portions 5a for the lead wires 4aand positioning protrusions 5b for fixing the terminals 5 to the formingdie.

The resin case 2 comprises nylon resin, for example. The resin case 2 isinsert-formed around one end of the temperature sensing element 1, thetwin leads 4 and the portions 5a and protrusions 5b of the terminals 5.The resin case 2 also forms a connector portion 2a exposing the otherends of the terminals 5 and integrally forms a stopper portion 3 in itsouter wall.

The stopper portion 3 has a complicated shape, as shown in FIG. 4, andforms a flexible arm 3a and a regulating surface 3b. The regulatingsurface 3b regulates the amount of deformation of the flexible arm 3a.The flexible arm 3a abuts the regulating surface 3b when the rotationaltorque of the stopper portion 3 engaged with an installing member 7, forexample, changes. The regulating surface 3b thereby limits the rotationof the stopper portion 3.

However, in the case of the above conventional techniques, it wasnecessary to have a process for enclosing the temperature sensingelement with resin as well as a process for forming the case, and a longtime was required for the resin enclosure. In this respect, the numberof processes could be reduced if the temperature sensing element isinsert-formed at the same time as the case is formed.

However, in order to arrange the temperature sensing element in apredetermined position in the case, it has been necessary to performinjection molding with the temperature sensing element supported bypositioning pins, for example, and to perform corrective action ofremoving the pins after forming is completed. As a result, traces of thepins are left in the case, causing the problem of water penetrating intothe interior of the case, thereby making it necessary to either limitthe temperature sensor's application or to perform a process of fillingin the traces.

SUMMARY OF THE INVENTION

The present invention has been made in order to solve the above-statedproblems encountered in the conventional art.

It is therefore an object of the present invention to provide a formingmethod for a temperature sensor which, as well as performing insertforming with a minimum of processes and in a short time with atemperature sensing element arranged in a predetermined position insidea-case, does not leave traces of pins which allow water to penetrate theinterior of the case. The present invention improves the conventionaltechnique disclosed in Published Unexamined Japanese Patent ApplicationNo. H6-129915 (described above) by improving the precision with whichthe temperature sensing element is disposed in a predetermined positioninside the case and minimizing inconsistencies in the thermal responsecharacteristic.

Additional objects, advantages and novel features of the invention willbe set forth in part in the description that follows, and in part willbecome apparent to those skilled in the art upon examination of thefollowing or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and attained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

In order to solve the above problems according to a first aspect of thepresent invention, a temperature sensor forming method is providedcomprising a first step of supporting a temperature sensing element bymeans of a first slide block and a second slide block, freely fitted inthe center of the first slide block, of a forming die, a second step ofinjecting a molten forming resin into the forming die and retracting thefirst slide block by injection pressure while the temperature sensingelement is supported by the second slide block, and a third step ofretracting the second block while injecting the molten forming resininto the forming die.

In accordance with a second aspect of the present invention, atemperature sensor forming die for resin forming is provided, comprisinga first slide block, a second slide block freely fitted in the center ofthe first slide block, and a temperature sensing element supported bythe first slide block and the second slide block, wherein a receivingarea in a sliding direction of the first slide block is set larger thana receiving area in a sliding direction of the second block with respectto a molten forming resin injected into a forming die, whereby only thefirst slide block is retractable by injection pressure when the moltenforming resin is first injected into the forming die, while thetemperature sensing element is being supported by the second slidingblock.

Since the present invention forms a temperature sensor by means of theabove forming method and forming die, it performs insert-forming with aminimum of processes and in a short time with a temperature sensingelement arranged in a predetermined position inside a case, and does notleave traces of pins which allow water to penetrate the interior of thecase. Also, it improves the precision with which the temperature sensingelement is disposed in a predetermined position inside the case andminimizes inconsistencies in the thermal response characteristic.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdescription, appended claims and accompanying drawings, wherein:

FIG. 1 is a cross-sectional view illustrating the first process of thepresent invention;

FIG. 2 is a cross-sectional view illustrating the second process of thepresent invention;

FIG. 3 is a cross-sectional view illustrating the third process of thepresent invention; and

FIG. 4 is a perspective view showing a conventional temperature sensor.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 to 3 illustrate preferred embodiments of a forming method andforming die for a temperature sensor according to the present invention.

It should be noted that a temperature sensor having the structure shownin FIG. 4 can be formed by the method and die according to FIGS. 1 to 3.In the following description of the present invention those componentsillustrated in FIG. 4 and having the same structures as in the prior artwill be described using the same reference numbers, and detaileddescriptions thereof will be omitted.

First, the process of insert-forming the temperature sensing element 1in the resin case 2 using a forming die 6 will be sequentiallydescribed. (1) First step: FIG. 1 shows a first step, illustrating astate wherein the temperature sensing element 1 is supported by a firstslide block 6c of the forming die 6 and a second slide block 6g fittedin the center of the first slide block 6c. This forming die 6 isprovided with a lower die 6a, an upper die 6b, the first slide block 6c,the second slide block 6g, and springs 6f and 6h. The first slide block6c further comprises a first support portion 6d for the positioningprotrusions 5b and a second support portion 6e for the temperaturesensing element 1.

In setting the temperature sensing element 1 in the forming die 6, theterminals 5 are first inserted in the lower die 6a, then the lower die6a is covered by the upper die 6b. At this time the terminals 5 arefixed by being sandwiched by the lower die 6a and the first supportportion 6d of the first slide block 6c, and the temperature sensingelement 1 is supported by being pushed by the rigidity of the twin leads4 against the second support portion 6e of the first slide block 6c anda tip 6i of the second slide block 6g. (2) Second step: FIG. 2 shows thesecond step following the first step, illustrating a state wherein thefirst slide block 6c is retracted due to the injection pressure ofmolten forming resin 2a.

The above molten forming resin 2a is pressure injected via a gate (notshown) into the space within the forming die 6 in which the temperaturesensing element 1 is set. This pressure is known as injection pressure.The pressure injected forming resin 2a flows in the directions of thearrows B and C of FIG. 2, and soon thereafter the injection pressureoperates the first slide block 6c. The first slide block 6c is retractedin the direction shown by the arrow D of FIG. 2.

In detail, the first slide block 6c is such that a receiving area S1 inthe sliding direction with respect to the molten forming resin 2ainjected into the forming die 6 is set larger than a receiving area S2in the sliding direction of the second slide block 6g. As a result, inthe initial step of injecting the molten forming resin 2a into theforming die 6, only the first slide block 6c can retract by means of theinjection pressure while the second slide block 6g is supporting thetemperature sensing element 1.

Thereby, the second support portion 6e of the first slide block 6c movesfrom position P to position Q shown in FIG. 2, and the molten formingresin 2a flows into this portion. At this time, the injection pressureof the molten forming resin 2a is in large part applied to the firstslide block 6c whose receiving area S1 is relatively large until theforming resin 2a fills every part of the space of the forming die 6, asa result of which initially only the first slide block 6c is retracted.Therefore, the second slide block 6g supports the temperature sensingelement 1 by way of its tip 6i. (3) Third step: FIG. 3 shows the thirdstep following the second step, illustrating a state wherein the secondslide block 6g is retracted while the molten forming resin 2a is beinginjected into the forming die 6.

Upon the above molten forming resin 2a filling every part of the spacein the forming die 6, the injection pressure of the molten forming resin2a is strongly applied to the second slide block 6g whose receiving areaS2 is relatively small. Immediately before the first slide block 6cfinishes moving to position Q in the second step, the first slide block6c engages with the second slide block 6g and the second slide block 6gmoves slightly toward the position P1 from the position P shown in FIG.2. As a result, a gap between the temperature sensing element 1 and thereceiving area S2 portion of the second slide block 6g widens. Themolten forming resin 2a penetrates into this gap and applies aninjection pressure to the receiving area S2 portion. The injectionpressure operates the second slide block 6g in the slide direction. As aresult, the second slide block 6g is retracted from positions P and P1to position Q subsequent to the retraction of the first slide block 6c.

In the case where the sequence that retracts the second sliding block 6gdoes not proceed well after only the first slide block 6c is retracted,the injection pressure in the third step may be increased over theinjection pressure in the second step, i.e., the injection pressure maybe modified in two stages. Of course it is also possible to retract thesecond slide block 6g using a negative pressure generating means,suitable drawing means, or the like.

It will be appreciated that the present invention is not limited to theexact construction and process steps that have been described above andillustrated in the accompanying drawings, and that various modificationsand changes can be made without departing from the scope and spiritthereof. It is intended that the scope of the invention only be limitedby the appended claims.

We claim:
 1. A temperature sensor forming method, comprising:a firststep of supporting a temperature sensing element by means of a firstslide block and a second slide block of a forming die, the second slideblock being freely fitted in a center of the first slide block andengaged with the temperature sensing element; a second step of injectinga molten forming resin into the forming die whereby an injectionpressure is created within the forming die, and retracting the firstslide block in a direction away from the temperature sensing element byapplying said injection pressure to a receiving area of the first slideblock while the temperature sensing element is supported by the secondslide block; and a third step of retracting the second slide block whileinjecting the molten forming resin into the forming die.
 2. Thetemperature sensor forming method according to claim 1, wherein saidthird step of retracting the second slide block further comprisesengaging the second slide block with said first slide block before thefirst slide block is fully retracted, whereby movement of said firstslide block causes said second slide block to move away from saidtemperature sensing element.
 3. The temperature sensor forming methodaccording to claim 1, wherein said third step comprises applying saidinjection pressure to a receiving area of said second slide block tocause said second slide block to be retracted.
 4. The temperature sensorforming method according to claim 1, wherein said first and second slideblocks are both retracted in a direction away from said temperaturesensing element in said second and third steps, respectively.
 5. Thetemperature sensor forming method according to claim 1, wherein saidsecond slide block is retracted in a direction away from saidtemperature sensing element in said third step.
 6. The temperaturesensor forming method according to claim 1, wherein said third stepfurther comprises increasing the injection pressure over the injectionpressure in said second step to facilitate retraction of said secondslide block.
 7. A temperature sensor forming method,comprising:providing a forming die having a first slide block and asecond slide block, said second slide block being freely fitted in acenter of the first slide block, and an injection pressure receivingarea in a sliding direction of said first slide block being larger thanan injection pressure receiving area in a sliding direction of saidsecond slide block; supporting a temperature sensing element in adesired position by engaging the temperature sensing element with saidfirst and second slide blocks; injecting a molten forming resin into theforming die whereby an injection pressure is created within said formingdie; retracting the first slide block in a direction away from saidtemperature sensing element by applying said injection pressure to theinjection pressure receiving area of said first slide block while thetemperature sensing element is supported by the second slide block; andretracting the second slide block in a direction away from saidtemperature sensing element while injecting the molten forming resininto the forming die.